A. Murky waters: which law is applicable to an assignment of a priority right?

Whether the transfer of a priority right is considered legally valid very much depends on the law that is applied to the transfer.

Let us take the example of a company “CA” incorporated in Canada that files a US patent application “USPA”. CA then decides to assign the priority right deriving from USPA to a company “DE” incorporated in Germany. DE subsequently files a European patent application EPA, claiming priority of USPA. The formal requirements of which law must the assignment of the priority right from CA to DE fulfil for it to be legally valid?

One might argue that the European Patent Convention is the applicable law since the convention priority is claimed for a European patent application. Conversely, one might say that the law of the first filing, i.e.US law must be applied. Finally, it is also conceivable to apply Canadian law since the initial owner of the priority right is a Canadian company.

In this opposition case, the European patent application resulting in the European patent in suit claimed convention priority from a Japanese patent application. The Japanese application and the subsequent European application were filed by different companies A and B, respectively, of the same corporate group. The validity of the priority claim was challenged on the basis that there was no valid assignment of the priority right from A to B prior to the filing of the European patent application.

The Board decided to apply, mutatis mutandis, the high formal requirements of Art. 72 EPC (the assignment of an EP application must be in writing and requires the signature of the parties to the contract) to the assignment of the priority right. Since the patentee could not provide a written document signed both by A and B, the Board declared the claimed priority invalid.

C. Decision “Fahrzeugscheibe” of the German Supreme Court dated April 16, 2013

In this nullity case, the European patent application resulting in the European patent in suit claimed convention priority from a German patent application. The German application and the subsequent European application were filed by different companies A and B, respectively, of the same corporate group. The validity of the priority claim was challenged on the basis that there was no valid assignment of the priority right from A to B prior to the filing of the European patent application.

One immediately notes that this case is analogous to the one decided by the EPO Board of Appeal. However, the German Supreme Court found the Board of Appeal’s approach to be ill-founded.

Rather, the German Supreme Court held that it is international private law which determines the applicable national law and thus the applicable formal requirements for a valid priority right assignment. Applying international private law, the German Supreme Court ruled that a priority right assignment is subject to the law of the state of first filing, i.e. in the present case German law.

According to German civil law, there are no particular formal requirements for the assignment of a priority right. Hence, a mutual oral agreement or an agreement manifested by conclusive action is sufficient for the priority right assignment to be valid.

Since the patentee was able to show that there had been a transfer of the priority right from A to B by conclusive action the German Supreme Court declared the claimed priority valid.

D. Conclusion

As the above decisions exemplify, the formal requirements for a valid priority right assignment vary substantially between countries and there is dissent between jurisdictions on the law that must be applied.

Accordingly, a priority right assignment should be carefully drafted in view of the national laws of all the countries where it is intended to file subsequent applications. At the very least, the assignment should be in writing, signed by all parties and clearly as well as separately state that the priority right itself is assigned.If you have questions on the above, feel free to contact Fabian Lieb.